The invention relates to an electric lamp provided with:
a light-transmitting envelope with an axis and a first and a second tubular end portion, a first and a second pole wire entering the lamp at the first end portion;
a light-transmitting gas-filled lamp vessel which is closed in a vacuumtight manner and is axially arranged in the envelope, into which lamp vessel a first and a second current conductor enter at mutually opposed locations, which current conductors are connected to an electric element in the lamp vessel and are fastened to the first and the second pole wire, respectively, outside the lamp vessel,
the second pole wire having a longitudinal portion which extends along the lamp vessel to the second end portion of the envelope and into which a Z-shaped first support portion merges at a first bend location,
which first support portion has a first support location adjacent the longitudinal portion and a second support location, and a central portion between said support locations, and
which first support portion is connected to a transverse portion which runs transversely through the envelope, to which the second current conductor is fastened, and by means of which a second support portion extending along the lamp vessel opposite the first support portion is connected to a support location,
said support portions bearing on the second end portion of the envelope.
Such an electric lamp is known from EP-B-0 476 461.
The second support portion in the known lamp has a shape which is identical to that of the first support portion, or is the mirrored image thereof. The first bend location has the purpose of keeping the first and the second support location at a distance from one another in a direction transverse to the axis. Both support portions have a central portion between their support locations which extends perpendicularly to the axis of the envelope. As a result, the support locations are spaced away from one another also in axial direction at each of the two support portions. The two central portions run parallel to one another.
The pole wires have the purpose not only to provide the lamp vessel with electric current, but also to bring and maintain the lamp vessel in a predetermined location in the envelope, also if the lamp has been subjected to shocks or vibrations. The first pole wire has a comparatively small length, and accordingly a sufficient stiffness for its mechanical purpose. The second pole wire extends along the lamp vessel and is longer than the first, and as a result it has a lower stiffness for a same given lateral dimension. The second pole wire must be supported by the envelope in the second end portion if it is to keep the lamp vessel fixed in the envelope.
The internal dimensions of the envelope of a batch of lamps of the same type is subject to fluctuations owing to tolerances in its manufacture. The dimensions of the second pole wire of such a batch of lamps are similarly subject to fluctuations, while in addition the shape of the pole wire may vary, which gives rise to skew dimensions. It was found that these factors may have the result that the second pole wire bears on the envelope in no more than three support locations, which do not lie distributed around the lamp vessel owing to the geometry of the second pole wire, or even in no more than two support locations. The lamp vessel is then insufficiently accurately positioned and insufficiently supported. Such a lamp will rattle when it is shaken.
It is an object of the invention to provide an electric lamp of the kind described in the opening paragraph which is of a simple and effective construction, whereby the lamp vessel is adequately supported.
According to the invention, this object is achieved in that the second support portion extends substantially in a plane through the axis towards its support location against the envelope.
The second pole wire has three support locations distributed over the circumference of the lamp vessel on account of its shape. The pole wire thus provides a reliable and effective support to and positioning of the lamp vessel. Dimension and shape tolerances of the second pole wire and the envelope are readily compensated for, so that rattling is avoided. The pole wire may readily be manufactured in one piece, which avoids welded joints in the pole wire.
In a favorable embodiment, the central portion of the first support portion crosses the axis at an acute angle and extends from the first support location to the second support location back to the longitudinal portion. This has the advantage that the first support portion is less stiff and more elastic than if it were perpendicular to the axis of the envelope, as in the known lamp. The first and the second support location can move relative to one another in the case of a lateral impact against the lamp. Since also the third support location, i.e. the support location of the second support portion, is resilient owing to the shape of this support location, all support locations are mutually resilient in this embodiment. The lamp vessel is resiliently supported around the axis. As a result, the lamp has a high shock resistance. Another advantage of this embodiment is that the two support locations of the first support portion, unlike in the known lamp, may be present at the same level in a plane which is substantially perpendicular to the axis. This enhances the symmetry of the construction.
It is favorable when the longitudinal portion has a second bend location where the second pole wire is bent towards the axis. This embodiment on the one hand renders it possible to have the longitudinal portion extend substantially straight along the envelope, while nevertheless sufficient room is created for the first support portion and for support locations thereof mutually spaced apart transversely to the axis, because the second bend location brings the first support portion closer to the axis. A sloping trend of the longitudinal portion adjacent the envelope renders possible a comparatively great distance to the lamp vessel, for example a locally convex lamp vessel, given certain chosen lateral dimensions, or a comparatively narrow envelope.
In a favorable modification, the first and the second bend location coincide. This modification limits the number of bending operations in the manufacture of the pole wire.
It is favorable when the support location of the second support portion lies substantially in a plane through the axis and through a point centrally located between the support locations of the first support portion. This measure promotes the symmetry of the support of the lamp vessel.
In an embodiment, the transverse portion has a straight fastening portion to which the second current conductor is fastened and a bent portion which retains the second support portion substantially in a plane through the axis and through a point centrally located between the support locations of the first support portion. This embodiment has the advantage that it renders it easier to mount the lamp vessel coaxially with the envelope.
A particularly favorable embodiment is one in which the support locations of the first support portion and the support location of the second support portion lie substantially in a plane which is perpendicular to the axis. The support locations in this case make contact with the envelope at least substantially simultaneously during mounting in the envelope. The risk of inadvertent warping is counteracted thereby, and the support portions will adapt themselves at least substantially simultaneously to the envelope if the second pole wire should have an excess dimension with respect to the envelope owing to tolerances.
The electric lamp according to the invention may be an incandescent lamp, for example a halogen incandescent lamp. The electric element in that case is an incandescent body, and the lamp vessel is filled with a gas comprising halogen, for example with xenon and hydrogen bromide. Alternatively, however, the lamp may be a discharge lamp, in which case the electric element is a pair of electrodes and the gas in the lamp vessel is ionizable.
The lamp vessel of the incandescent or discharge lamp will usually be made of quartz glass, but it may alternatively be made of a ceramic material such as, for example, polycrystalline aluminum oxide. The discharge lamp has an ionizable filling such as, for example, mercury, sodium, metal halide, or combinations thereof, with a rare gas as a starter gas. The lamp vessel may be tubular, or alternatively may enclose a rounded, for example spherical or oval space.
The envelope may be tubular or may be rounded between its end portions. The envelope is usually made of quartz glass or hard glass. The envelope may be closed in a vacuumtight manner, for example with a pinch seal at the first end portion. The envelope may be filled with gas or may be evacuated. The envelope may support a lamp cap at the first end portion, for example made of ceramic material and having contacts to which the pole wires are electrically connected.